Normally you place these in a file called AssemblyInfo.vb and compile it into your assembly (Visual Studio will generate this for you from the settings you set if you go to project settings - Application | Assembly Information. Have a look in the project folder, there is by default a sub-folder with the same name as your project and in there is the aforementioned .vb file).

If you want, however, to update a precompiled .NET assembly I think you would need to decompile it, change the attributes in the manifest you want to change and re-compile it. You can do this using the ildasm tool. If an assembly is strong named you will not be able to recompile it using the same strong name than it was compiled with of course.

Properties like comment or title are not provided for all files equally, because they are not stored by the filesystem but come from the file itself. Therefore they must be part of the file format and not all file formats provide such properties. Indeed, many file formats don't provide any properties at all (e.g. .txt). Even when the file format supports some properties, Windows needs a custom property handler installed to extract, interpret and possibly modify them.

Executables provide some read-only properties through the version information resource. However they cannot and should not be changed, because this will mess up file checksums, break digital signatures etc.